The present invention relates to communications protocols, and particularly to communications protocols suitable for a half duplex system involving one-to-many and many-to-one node communication topologies.
The invention relates to data transmission system, typically in a geographically limited framework, also called wireless personal area network (W-PAN). The invention finds particular application at millimeter wave frequencies, typically in the 60 GHz band for communication node interconnection. At such frequencies, electromagnetic signals have a behavior close to that of light, and so preferably require a direct transmission without reflection, ie. Line of Sight (LOS). The spread of these waves is characterized by rapid attenuation of the signal strength. W-PAN in the 60 GHz range is applicable where very high throughputs are required, and where bandwidth is at a premium.
Wireless AN (audio/video) applications are now increasingly numerous and require ever higher data bit rates of the order of some Gigabits per second (here below denoted as Gbps) and an increasingly higher quality of service. W-PAN millimeter type networks are particularly well suited to this type of application. Indeed, the authorized band around a carrier frequency of 60 GHz offers a wide bandwidth thus enabling the transportation of a large quantity of data. Besides, the radio range of such systems is limited to about ten meters, favoring the re-utilization of the frequencies in time and space.
However, the power of the directly transmitted signals is attenuated rapidly as they are propagated. In order to improve signal to noise ratio several methods have been proposed. Antenna diversity uses two or more antennas to improve the quality and reliability of a wireless link. Multiple spatially separated antennas offer a receiver several observations of the same signal. Each antenna will experience a different interference environment, which is to say that each antenna can provide a physically distinct communication channel. Thus, if one antenna is experiencing a deep fade, it is possible that another has a sufficient signal. Collectively such a system can provide a robust link. Such spatial diversity may be observed in receiving systems (diversity reception), as well as transmitting systems (transmit diversity).
Use of multiple antennas to transmit and receive the same information may however increase complexity of communication protocol and compromise bandwidth efficiency to some extent.